Thousands of Egyptian anti-government protesters have clashed with police in Cairo.
Police have been responding with rubber bullets, tear gas and water cannons to disperse them.
Water cannons were also turned on Egypt's pro-democracy leader Mohamed ElBaradei and his supporters as they joined the latest wave of protests after Friday prayers.
Police used batons to beat some of Mr ElBaradei's supporters, who surrounded him to protect him.
Clusters of riot police with helmets and shields were stationed around the city, at the entrances to bridges across the Nile and other key intersections. Near the city's main Tahrir Square, hundreds of riot police moved in, anticipating the arrival of thousands of protesters.
At Ramsis square in the heart of the city, thousands of protesters clashed with police as they left the al-Nur mosque after prayers. Tear gas was fired inside the mosque, where women were taking refuge.
In the prosperous Mohandiseen district, at least 10,000 people marched towards the city centre chanting "down, down with Mubarak".
Regional television stations reported clashes between thousands of protesters and police in several other major Egyptian cities, including the Mediterranean port city of Alexandria, Minya and Assiut south of Cairo and al-Arish in the Sinai peninsula.
Internet and mobile phone services were down and telecom experts said Egyptian authorities could have engineered the cut off with a simple change to the instructions for the companies' networking equipment to disrupt the organisation of demonstrations.
The developments were a sign that president Hosni Mubarak's regime is toughening its crackdown following the biggest protests in years against his nearly 30-year rule. Mr Mubarak, 82, has not been seen in public or heard from since the protests began on Tuesday.